Answers

You would not be evicted from your apartment because you purchased a house.

Your landlord is evicting you for some other reason. You should look at the notice signed and issued by your landlord concerning your being required to move. It did not say you were being asked to leave because you purchased a house.

You purchasing a house is not a legal reason to be asked to move by your landlord.

In certain situations, yes. It would not be for merely buying property. It could be that your rent is based on your reported income and assets, even possibly subsidized. If you no longer are below the income and assets maximums for qualification (you earn or own too much, and being able to buy a house will probably do it), you can be evicted.